"We review the latest advances in the production and state-of-the art characterization of B- and N-doped carbon nanotubes (CNTs) and nanofibers. We briefly discuss different approaches to producing these novel doped nano-systems. The use of high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), scanning tunneling spectroscopy (STS), Raman spectroscopy, and allied techniques to characterize these doped systems is reviewed. The field emission properties as well as some applications to the fabrication of novel polymer composites, Li+ batteries, and gas sensors are also discussed. It is clear that these materials possess outstanding properties when compared with pure CNTs, and it is foreseen that these systems will revolutionize some aspects of nanotube science and technology, thus opening a vast field of experimental and theoretical research."